Flame visualization control for a burner including a perforated flame holder

ABSTRACT

A combustion system includes a perforated flame holder, a camera, and a control circuit. The perforated flame holder sustains a combustion reaction within the perforated flame holder. The image capture device takes a plurality of images of the combustion reaction. The control circuit produces from the images an averaged image and adjusts the combustion reaction based on the adjusted image.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation-in-Part of co-pending U.S.patent application Ser. No. 15/132,807, entitled “FLAME VISUALIZATIONCONTROL FOR A BURNER INCLUDING A PERFORATED FLAME HOLDER,” filed Apr.19, 2016 (docket number 2651-281-03). U.S. patent application Ser. No.15/132,807 is a Continuation-in-Part of International PCT PatentApplication No. PCT/US2014/060534, entitled “FLAME VISUALIZATION CONTROLFOR ELECTRODYNAMIC COMBUSTION CONTROL,” filed Oct. 14, 2014 (docketnumber 2651-130-04), now expired. International PCT Patent ApplicationNo. PCT/US2014/060534 claims priority benefit from U.S. ProvisionalPatent Application No. 61/890,668, entitled “ELECTRODYNAMIC COMBUSTIONCONTROL (ECC) TECHNOLOGY FOR BIOMASS AND COAL SYSTEMS,” filed Oct. 14,2013 (docket number 2651-201-02), now expired. Each of the foregoingapplications, to the extent not inconsistent with the disclosure herein,is incorporated by reference.

SUMMARY

According to an embodiment, a combustion system includes a fuel nozzleconfigured to output fuel and oxidant and a perforated flame holder. Theperforated flame holder includes a first face, a second face, and aplurality of perforations extending between the first face and thesecond face, the first face being positioned to receive the fuel andoxidant from the fuel and oxidant source, the perforated flame holderbeing configured to sustain a combustion reaction of the fuel andoxidant within the perforations. The combustion system further includesan image capture device configured to capture a plurality of images ofthe combustion reaction and a control circuit configured to produce fromthe plurality of images an average image of the combustion reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a combustion system including a perforatedflame holder and a camera, according to an embodiment.

FIG. 2 is a diagram of a combustion system including a perforated flameholder, according to an embodiment.

FIG. 3 is a cross-sectional diagram of a perforated flame holder,according to an embodiment.

FIG. 4 is a flow diagram for a process for operating a combustion systemincluding a perforated flame holder, according to an embodiment.

FIG. 5A is a diagram of a combustion system including a perforated flameholder and an image capture device, according to an embodiment.

FIGS. 5B-5D are diagrams of a combustion system including a combustionreaction in various positions, according to an embodiment.

FIG. 5E is an illustration of an averaged image of the combustionreaction from FIGS. 5B-5D, according to an embodiment.

FIG. 6A is a diagram of a combustion system including a perforated flameholder and an electrocapacitive tomography system, according to anembodiment.

FIG. 6B is a top view of the perforated flame holder and theelectrocapacitive tomography system, according to an embodiment.

FIG. 7A is a diagram of a combustion system including a perforated flameholder and an electromagnetic induction tomography system, according toan embodiment.

FIG. 7B is a top view of the perforated flame holder and theelectromagnetic induction tomography system, according to an embodiment.

FIG. 7C is a side view of an inductor coil of the electromagneticinduction tomography device, according to an embodiment.

FIG. 8A is an enlarged side-sectional view of a portion of a perforatedflame holder and an electroresistive tomography system, according to anembodiment.

FIG. 8B is a perspective view of a portion of the perforated flameholder and electroresistive tomography system of FIG. 8A, according toan embodiment.

FIG. 9 is a diagram of a combustion system including a perforated flameholder and an image capture device, according to an embodiment.

FIG. 10 is a graph of the intensity of light emitted from a perforatedflame holder versus the wavelength of light, according to an embodiment.

FIG. 11 is a flow diagram for a process for operating a combustionsystem including a perforated flame holder and an image capture device,according to one embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. Other embodiments may be used and/or other changesmay be made without departing from the spirit or scope of thedisclosure.

As used herein, the term electrocapacitive tomography (ECT) shall beunderstood as described. ECT sensing may be fundamentally capacitive, ormay additionally or alternatively be made to actually measure aconductance, a resistance, an impedance, or other electrical parameter.ECT may include a plurality of sensor channels, such as may be producedby moving a sensor or using a sensor array, such as may be seen in morefamiliar (e.g., medical) tomography systems. Additionally oralternatively, an ECT system may include a range of sensor channels aslow as a single channel defined by two electrodes positioned relative toa sensed region (e.g., a flame-holding region, a blow-off region, aflash-back region, a flue gas region, a pilot flame region, etc.).Unless context dictates otherwise, disclosure and claims herein shall beaccorded this broad meaning.

FIG. 1 is a block diagram of a combustion system 100 according to oneembodiment. The combustion system 100 includes a fuel and oxidant source101, a perforated flame holder 102, a control circuit 103, an imagecapture device 105, a memory 107, and a display 109.

The fuel and oxidant source 101 is configured to output fuel and oxidantonto the perforated flame holder 102. According to an embodiment, theperforated flame holder 102 includes a first face, a second face, and aplurality of perforations extending between the first face and thesecond face. A combustion reaction of the fuel and oxidant is sustainedprimarily within the perforations.

According to an embodiment, in some circumstances it may be desirable tokeep the perforated flame holder 102 within a selected temperaturerange. Additionally, in some circumstances it may be desirable to have aparticular distribution of temperature throughout the perforated flameholder. However, it is possible in some instances for the combustionreaction to take on undesirable characteristics. For example, thecombustion reaction can become too hot, too cool, unevenly distributedthroughout the perforated flame holder, too much of the combustionreaction may occur above or below the perforated flame holder 102, orother possible problematic characteristics.

According to an embodiment, the image capture device 105 is positionedto capture images of the combustion reaction. The captured images caninclude visible spectrum imaging, infrared imaging, ultraviolet imaging,or a combination of these or other types of images. The image capturedevice 105 can rapidly capture multiple successive images or can captureindividual images for display or analysis. The images can provide anindication of the location of the combustion reaction, the temperatureof the combustion reaction and/or the perforated flame holder 102, thedistribution of the combustion reaction within the perforated flameholder 102, how much of the combustion reaction is above or below theperforated flame holder 102, or other aspects of the combustion reactionor perforated flame holder 102.

Because of the fluidity of combustion reaction characteristics, it canbe very difficult to determine whether or not a particular imagecorresponds to a selected combustion reaction shape or selectedcombustion reaction characteristics. The inventors discovered that, byaveraging a number of successive image frames, a truer representation ofcombustion reaction characteristics can be obtained. The averaged imageframes can thus be used for feedback control of the combustion system100.

In one embodiment, the image capture device 105 provides the pluralityof images to the control circuit 103. The control circuit 103 producesfrom the plurality of images an averaged image of the combustionreaction. The averaged image provides information about the averageposition, distribution, temperature profile, and/or othercharacteristics of the combustion reaction and/or the perforated flameholder 102. The averaged image can therefore give an indication of howthe combustion reaction is distributed within the perforated flameholder 102, whether excessive portions of the combustion reaction areabove or below the perforated flame holder 102, the temperaturedistribution of the perforated flame holder, how much heat is outputfrom the perforated flame holder 102, or other characteristics of thecombustion reaction and/or the perforated flame holder 102. The controlcircuit 103 can adjust the combustion reaction based on the averagedimage in order to obtain a combustion reaction with selectedcharacteristics. Additionally or alternatively the control circuit 103can adjust the combustion reaction based on analysis of a single imageor a plurality of images instead of or in addition to an averaged image.

The control circuit 103 can adjust the combustion reaction in a varietyof ways. In one embodiment, the control circuit can adjust thecombustion reaction by stopping the output of fuel and oxidant from thefuel and oxidant source 101. Stopping the output of fuel and oxidantwill stop the combustion reaction. In one embodiment, the controlcircuit 103 can control the fuel and oxidant source 101 to adjust thefuel and oxidant coming from the fuel and oxidant source 101. Inparticular, the control circuit 103 can adjust the velocity of the fuel,the flow rate of the fuel, the direction of flow of the fuel, or theconcentration of fuel in the fuel and oxidant mixture in order to obtaina combustion reaction with selected characteristics. The control circuit103 may also adjust the air or air/fuel ratio or one or more othercombustion control parameters. In one example, the image capture devicecaptures one or more images of the perforated flame holder 102 andprovides them to the control circuit 103. The control circuit analyzesthe one or more images, or an averaged image based on the one or moreimages. The one or more images indicate that some portions of theperforated flame holder 102 are significantly hotter than other portionsof the perforated flame holder. This may indicate that the fuel andoxidant are not being received uniformly across the perforated flameholder 102. The control circuit 103 can adjust an output of the fuel andoxidant to more evenly distribute the fuel and oxidant to the perforatedflame holder 102. The control circuit 103 can adjust the output of fueland oxidant based on analysis of a single image, multiple images, and/oran averaged image created from multiple images.

In one embodiment, the control circuit 103 can determine combustionreaction characteristics based on the colors or wavelengths of lightassociated with the combustion reaction at the various areas of theperforated flame holder. The one or more images can indicate visiblespectrum colors or wavelengths outside the visible spectrum, such asultraviolet or infrared wavelengths.

In one embodiment, the image may indicate that the perforated flameholder 102 is darker than normal. This can indicate that a significantportion of the combustion reaction occurs in blue flames above theperforated flame holder 102. In this case the control circuit can reducethe heat load. In one example adjusting the heat load includes reducingwater flow to steam tubes. In one embodiment the fuel and oxidant source101 can include one or more fuel nozzles each having one or moreorifices. The control circuit can reduce fuel velocity by switching tolarger orifice nozzles or by outputting the same amount of fuel throughmore nozzles. In one embodiment the control circuit can change the fuelmix to a higher speed fuel, for example by adding hydrogen.

In one embodiment, the control circuit 103 outputs the one or moreimages, or the averaged image, for display on the display 109. Atechnician of the combustion system 100 can analyze the one or moreimages on the display, or the averaged image, and can adjust thecombustion reaction based on the one or more images or the averagedimage. The technician can then adjust the parameters of the combustionsystem 100 to attain desired characteristics of the combustion reaction.

In one embodiment, the memory 107 stores combustion reaction referencedata. The combustion reaction reference data may be collected from theas-new or as-desired operating condition to be stored as the combustionreaction reference data. After the control circuit 103 has produced theaveraged image of the combustion reaction, the control circuit 103 cancompare the averaged image to the reference data stored in the memory107. In this way the control circuit 103 can determine if the combustionreaction has characteristics in accordance with characteristics selectedby an operator of the combustion system 100 or stored in the memory 107.Based on the comparison between the averaged image and the referencedata stored in the memory 107, the control circuit 103 can adjust thecombustion reaction to achieve the selected characteristics.

After the control circuit 103 has adjusted the combustion reaction, theimage capture device 105 captures another series of images of thecombustion reaction. The control circuit 103 produces another averagedimage of the combustion reaction from the most recent series of imagescaptured by the image capture device 105. The control circuit 103compares the new averaged image to the reference data stored in thememory 107. If the comparison indicates that the combustion reaction hascharacteristics substantially in accordance with the selectedcharacteristics, then the control circuit 103 does not adjust thecombustion reaction. If the comparison indicates that the combustionreaction still has not achieved the selected characteristics, then thecontrol circuit 103 can further adjust the combustion reaction.

In one embodiment, the reference data stored in the memory 107 includesa plurality of reference images of the combustion reaction. The controlcircuit 103 compares the averaged image of the combustion reaction toone or more of the reference images. Based on the comparison of theaveraged image to the reference images, the control circuit 103 canadjust the combustion reaction.

In one embodiment, the desired characteristics of the combustionreaction correspond to a particular target reference image stored in thememory 107. The control circuit 103 compares the averaged image to thetarget reference image corresponding to the selected characteristics forthe combustion reaction. The control circuit 103 then adjusts thecombustion reaction based on the comparison between the averaged imageand the target reference image in order to conform the combustionreaction to the target reference image.

The image capture device 105 can be an infrared camera, a visible lightcamera, an ultraviolet light camera, a flame scanner or any othersuitable image capture device that can capture images of a combustionreaction or output an indication of the characteristics of thecombustion reaction.

In one embodiment, the image capture device 105 is a video camera thatrecords a video of the combustion reaction. The control circuit 103 thenaverages individual frames of the video to produce the averaged image.

In one embodiment, the image capture device 105 includes an electricalcapacitance tomography device. The electrical capacitance tomographydevice includes a plurality of electrodes positioned at selectedlocations adjacent to the perforated flame holder 102. The electricaltomography device makes a plurality of images representing slices of theperforated flame holder based on the capacitances between theelectrodes. These images can give an indication of a concentration orflow of fuel, oxidant, and flue gasses at various locations in theperforated flame holder 102 based on the dielectric constant at thevarious locations of the perforated flame holder 102. The images canalso give an indication of the temperature at various locations withinthe perforated flame holder 102. The control circuit 103 can analyze theimages and adjust the combustion reaction based on the images.

The control circuit 103 can adjust the combustion reaction in a varietyof ways. In one embodiment, the control circuit 103 can control the fueland oxidant source 101 to adjust the fuel and oxidant coming from thefuel and oxidant source 101. In particular, the control circuit 103 canadjust the velocity of the fuel, the flow rate of the fuel, thedirection of flow of the fuel, or the concentration of fuel in the fueland oxidant mixture in order to obtain the combustion reaction withselected characteristics. The control circuit 103 may also adjust theair or air/fuel ratio or the one or more other combustion controlparameters.

In one embodiment the image capture device 105 includes multiple imagecapture devices disposed at various positions relative to the perforatedflame holder 102. For example, the image capture device 105 can includea first image capture device positioned to capture an image of a topsurface of the perforated flame holder and a second image capture devicepositioned to capture an image of the fuel and oxidant source and/or abottom surface of the perforated flame holder. The second image capturedevice can capture an image of a startup flame configured to preheat theperforated flame holder 102. Additionally or alternatively the secondimage capture device can capture an image that indicates whether thecombustion reaction is near the fuel and oxidant source 101. The controlcircuit or a technician can adjust the combustion reaction or thepreheating flame based on the image from the second image capturedevice.

FIG. 2 is a simplified diagram of a burner system 200 including aperforated flame holder 102 configured to hold a combustion reaction,according to an embodiment. As used herein, the terms perforated flameholder, perforated reaction holder, porous flame holder, porous reactionholder, duplex, and duplex tile shall be considered synonymous unlessfurther definition is provided.

Experiments performed by the inventors have shown that perforated flameholders 102 described herein can support very clean combustion.Specifically, in experimental use of systems 200 ranging from pilotscale to full scale, output of oxides of nitrogen (NOx) was measured torange from low single digit parts per million (ppm) down to undetectable(less than 1 ppm) concentration of NOx at the stack. These remarkableresults were measured at 3% (dry) oxygen (O₂) concentration withundetectable carbon monoxide (CO) at stack temperatures typical ofindustrial furnace applications (1400-1600° F.). Moreover, these resultsdid not require any extraordinary measures such as selective catalyticreduction (SCR), selective non-catalytic reduction (SNCR), water/steaminjection, external flue gas recirculation (FGR), or other heroicextremes that may be required for conventional burners to even approachsuch clean combustion.

According to embodiments, the burner system 200 includes a fuel andoxidant source 101 disposed to output fuel and oxidant into a combustionvolume 204 to form a fuel and oxidant mixture 206. As used herein, theterms fuel and oxidant mixture and fuel stream may be usedinterchangeably and considered synonymous depending on the context,unless further definition is provided. As used herein, the termscombustion volume, combustion chamber, furnace volume, and the likeshall be considered synonymous unless further definition is provided.The perforated flame holder 102 is disposed in the combustion volume 204and positioned to receive the fuel and oxidant mixture 206.

FIG. 3 is a side sectional diagram 300 of a portion of the perforatedflame holder 102 of FIGS. 1 and 2, according to an embodiment. Referringto FIGS. 2 and 3, the perforated flame holder 102 includes a perforatedflame holder body 208 defining a plurality of perforations 210 alignedto receive the fuel and oxidant mixture 206 from the fuel and oxidantsource 101. As used herein, the terms perforation, pore, aperture,elongated aperture, and the like, in the context of the perforated flameholder 102, shall be considered synonymous unless further definition isprovided. The perforations 210 are configured to collectively hold acombustion reaction 302 supported by the fuel and oxidant mixture 206.

The fuel can include hydrogen, a hydrocarbon gas, a vaporizedhydrocarbon liquid, an atomized hydrocarbon liquid, or a powdered orpulverized solid. The fuel can be a single species or can include amixture of gas(es), vapor(s), atomized liquid(s), and/or pulverizedsolid(s). For example, in a process heater application the fuel caninclude fuel gas or byproducts from the process that include carbonmonoxide (CO), hydrogen (H₂), and methane (CH₄). In another application,the fuel can include natural gas (mostly CH₄) or propane (C₃H₈). Inanother application, the fuel can include #2 fuel oil or #6 fuel oil.Dual fuel applications and flexible fuel applications are similarlycontemplated by the inventors. The oxidant can include oxygen carried byair, flue gas, and/or can include another oxidant, either pure orcarried by a carrier gas. The terms oxidant and oxidizer shall beconsidered synonymous herein.

According to an embodiment, the perforated flame holder body 208 can bebounded by an input face 212 disposed to receive the fuel and oxidantmixture 206, an output face 214 facing away from the fuel and oxidantsource 101, and a peripheral surface 216 defining a lateral extent ofthe perforated flame holder 102. The plurality of perforations 210 whichare defined by the perforated flame holder body 208 extend from theinput face 212 to the output face 214. The plurality of perforations 210can receive the fuel and oxidant mixture 206 at the input face 212. Thefuel and oxidant mixture 206 can then combust in or near the pluralityof perforations 210 and combustion products can exit the plurality ofperforations 210 at or near the output face 214.

According to an embodiment, the perforated flame holder 102 isconfigured to hold a majority of the combustion reaction 302 within theperforations 210. For example, on a steady-state basis, more than halfthe molecules of fuel output into the combustion volume 204 by the fueland oxidant source 101 may be converted to combustion products betweenthe input face 212 and the output face 214 of the perforated flameholder 102. According to an alternative interpretation, more than halfof the heat or thermal energy output by the combustion reaction 302 maybe output between the input face 212 and the output face 214 of theperforated flame holder 102. As used herein, the terms heat, heatenergy, and thermal energy shall be considered synonymous unless furtherdefinition is provided. As used above, heat energy and thermal energyrefer generally to the released chemical energy initially held byreactants during the combustion reaction 302. As used elsewhere herein,heat, heat energy and thermal energy correspond to a detectabletemperature rise undergone by real bodies characterized by heatcapacities. Under nominal operating conditions, the perforations 210 canbe configured to collectively hold at least 80% of the combustionreaction 302 between the input face 212 and the output face 214 of theperforated flame holder 102. In some experiments, the inventors produceda combustion reaction 302 that was apparently wholly contained in theperforations 210 between the input face 212 and the output face 214 ofthe perforated flame holder 102. According to an alternativeinterpretation, the perforated flame holder 102 can support combustionbetween the input face 212 and output face 214 when combustion is“time-averaged.” For example, during transients, such as before theperforated flame holder 102 is fully heated, or if too high a (cooling)load is placed on the system, the combustion may travel somewhatdownstream from the output face 214 of the perforated flame holder 102.Alternatively, if the cooling load is relatively low and/or the furnacetemperature reaches a high level, the combustion may travel somewhatupstream of the input face 212 of the perforated flame holder 102.

While a “flame” is described in a manner intended for ease ofdescription, it should be understood that in some instances, no visibleflame is present. Combustion occurs primarily within the perforations210, but the “glow” of combustion heat is dominated by a visible glow ofthe perforated flame holder 102 itself. In other instances, theinventors have noted transient “huffing” or “flashback” wherein avisible flame momentarily ignites in a region lying between the inputface 212 of the perforated flame holder 102 and the fuel nozzle 218,within the dilution region D_(D). Such transient huffing or flashback isgenerally short in duration such that, on a time-averaged basis, amajority of combustion occurs within the perforations 210 of theperforated flame holder 102, between the input face 212 and the outputface 214. In still other instances, the inventors have noted apparentcombustion occurring downstream from the output face 214 of theperforated flame holder 102, but still a majority of combustion occurredwithin the perforated flame holder 102 as evidenced by continued visibleglow from the perforated flame holder 102 that was observed.

The perforated flame holder 102 can be configured to receive heat fromthe combustion reaction 302 and output a portion of the received heat asthermal radiation 304 to heat-receiving structures (e.g., furnace wallsand/or radiant section working fluid tubes) in or adjacent to thecombustion volume 204. As used herein, terms such as radiation, thermalradiation, radiant heat, heat radiation, etc. are to be construed asbeing substantially synonymous, unless further definition is provided.Specifically, such terms refer to blackbody-type radiation ofelectromagnetic energy, primarily at infrared wavelengths, but also atvisible wavelengths owing to elevated temperature of the perforatedflame holder body 208.

Referring especially to FIG. 3, the perforated flame holder 102 outputsanother portion of the received heat to the fuel and oxidant mixture 206received at the input face 212 of the perforated flame holder 102. Theperforated flame holder body 208 may receive heat from the combustionreaction 302 at least in heat receiving regions 306 of perforation walls308. Experimental evidence has suggested to the inventors that theposition of the heat receiving regions 306, or at least the positioncorresponding to a maximum rate of receipt of heat, can vary along thelength of the perforation walls 308. In some experiments, the locationof maximum receipt of heat was apparently between ⅓ and ½ of thedistance from the input face 212 to the output face 214 (i.e., somewhatnearer to the input face 212 than to the output face 214). The inventorscontemplate that the heat receiving regions 306 may lie nearer to theoutput face 214 of the perforated flame holder 102 under otherconditions. Most probably, there is no clearly defined edge of the heatreceiving regions 306 (or for that matter, the heat output regions 310,described below). For ease of understanding, the heat receiving regions306 and the heat output regions 310 will be described as particularregions 306, 310.

The perforated flame holder body 208 can be characterized by a heatcapacity. The perforated flame holder body 208 may hold thermal energyfrom the combustion reaction 302 in an amount corresponding to the heatcapacity multiplied by temperature rise, and transfer the thermal energyfrom the heat receiving regions 306 to heat output regions 310 of theperforation walls 308. Generally, the heat output regions 310 are nearerto the input face 212 than are the heat receiving regions 306. Accordingto one interpretation, the perforated flame holder body 208 can transferheat from the heat receiving regions 306 to the heat output regions 310via thermal radiation, depicted graphically as 304. According to anotherinterpretation, the perforated flame holder body 208 can transfer heatfrom the heat receiving regions 306 to the heat output regions 310 viaheat conduction along heat conduction paths 312. The inventorscontemplate that multiple heat transfer mechanisms including conduction,radiation, and possibly convection may be operative in transferring heatfrom the heat receiving regions 306 to the heat output regions 310. Inthis way, the perforated flame holder 102 may act as a heat source tomaintain the combustion reaction 302, even under conditions where acombustion reaction 302 would not be stable when supported from aconventional flame holder.

The inventors believe that the perforated flame holder 102 causes thecombustion reaction 302 to begin within thermal boundary layers 314formed adjacent to walls 308 of the perforations 210. Insofar ascombustion is generally understood to include a large number ofindividual reactions, and since a large portion of combustion energy isreleased within the perforated flame holder 102, it is apparent that atleast a majority of the individual reactions occur within the perforatedflame holder 102. As the relatively cool fuel and oxidant mixture 206approaches the input face 212, the flow is split into portions thatrespectively travel through individual perforations 210. The hotperforated flame holder body 208 transfers heat to the fluid, notablywithin thermal boundary layers 314 that progressively thicken as moreand more heat is transferred to the incoming fuel and oxidant mixture206. After reaching a combustion temperature (e.g., the auto-ignitiontemperature of the fuel), the reactants continue to flow while achemical ignition delay time elapses, over which time the combustionreaction 302 occurs. Accordingly, the combustion reaction 302 is shownas occurring within the thermal boundary layers 314. As flow progresses,the thermal boundary layers 314 merge at a merger point 316. Ideally,the merger point 316 lies between the input face 212 and output face 214that define the ends of the perforations 210. At some position along thelength of a perforation 210, the combustion reaction 302 outputs moreheat to the perforated flame holder body 208 than it receives from theperforated flame holder body 208. The heat is received at the heatreceiving region 306, is held by the perforated flame holder body 208,and is transported to the heat output region 310 nearer to the inputface 212, where the heat is transferred into the cool reactants (and anyincluded diluent) to bring the reactants to the ignition temperature.

In an embodiment, each of the perforations 210 is characterized by alength L defined as a reaction fluid propagation path length between theinput face 212 and the output face 214 of the perforated flame holder102. As used herein, the term reaction fluid refers to matter thattravels through a perforation 210. Near the input face 212, the reactionfluid includes the fuel and oxidant mixture 206 (optionally includingnitrogen, flue gas, and/or other “non-reactive” species). Within thecombustion reaction region, the reaction fluid may include plasmaassociated with the combustion reaction 302, molecules of reactants andtheir constituent parts, any non-reactive species, reactionintermediates (including transition states), and reaction products. Nearthe output face 214, the reaction fluid may include reaction productsand byproducts, non-reactive gas, and excess oxidant.

The plurality of perforations 210 can be each characterized by atransverse dimension D between opposing perforation walls 308. Theinventors have found that stable combustion can be maintained in theperforated flame holder 102 if the length L of each perforation 210 isat least four times the transverse dimension D of the perforation. Inother embodiments, the length L can be greater than six times thetransverse dimension D. For example, experiments have been run where Lis at least eight, at least twelve, at least sixteen, and at leasttwenty-four times the transverse dimension D. Preferably, the length Lis sufficiently long for thermal boundary layers 314 to form adjacent tothe perforation walls 308 in a reaction fluid flowing through theperforations 210 to converge at merger points 316 within theperforations 210 between the input face 212 and the output face 214 ofthe perforated flame holder 102. In experiments, the inventors havefound L/D ratios between 12 and 48 to work well (i.e., produce low NOx,produce low CO, and maintain stable combustion).

The perforated flame holder body 208 can be configured to convey heatbetween adjacent perforations 210. The heat conveyed between adjacentperforations 210 can be selected to cause heat output from thecombustion reaction portion 302 in a first perforation 210 to supplyheat to stabilize a combustion reaction portion 302 in an adjacentperforation 210.

Referring especially to FIG. 2, the fuel and oxidant source 101 canfurther include a fuel nozzle 218, configured to output fuel, and anoxidant source 220 configured to output a fluid including the oxidant.For example, the fuel nozzle 218 can be configured to output pure fuel.The oxidant source 220 can be configured to output combustion aircarrying oxygen, and optionally, flue gas.

The perforated flame holder 102 can be held by a perforated flame holdersupport structure 222 configured to hold the perforated flame holder 102at a dilution distance D_(D) away from the fuel nozzle 218. The fuelnozzle 218 can be configured to emit a fuel jet selected to entrain theoxidant to form the fuel and oxidant mixture 206 as the fuel jet andoxidant travel along a path to the perforated flame holder 102 throughthe dilution distance D_(D) between the fuel nozzle 218 and theperforated flame holder 102. Additionally or alternatively (particularlywhen a blower is used to deliver oxidant contained in combustion air),the oxidant or combustion air source can be configured to entrain thefuel and the fuel and oxidant travel through the dilution distanceD_(D). In some embodiments, a flue gas recirculation path 224 can beprovided. Additionally or alternatively, the fuel nozzle 218 can beconfigured to emit a fuel jet selected to entrain the oxidant and toentrain flue gas as the fuel jet travels through the dilution distanceD_(D) between the fuel nozzle 218 and the input face 212 of theperforated flame holder 102.

The fuel nozzle 218 can be configured to emit the fuel through one ormore fuel orifices 226 having an inside diameter dimension that isreferred to as “nozzle diameter.” The perforated flame holder supportstructure 222 can support the perforated flame holder 102 to receive thefuel and oxidant mixture 206 at the distance D_(D) away from the fuelnozzle 218 greater than 20 times the nozzle diameter. In anotherembodiment, the perforated flame holder 102 is disposed to receive thefuel and oxidant mixture 206 at the distance D_(D) away from the fuelnozzle 218 between 100 times and 1100 times the nozzle diameter.Preferably, the perforated flame holder support structure 222 isconfigured to hold the perforated flame holder 102 at a distance about200 times or more of the nozzle diameter away from the fuel nozzle 218.When the fuel and oxidant mixture 206 travels about 200 times the nozzlediameter or more, the mixture is sufficiently homogenized to cause thecombustion reaction 302 to produce minimal NOx.

The fuel and oxidant source 101 can alternatively include a premix fueland oxidant source, according to an embodiment. A premix fuel andoxidant source can include a premix chamber (not shown), a fuel nozzleconfigured to output fuel into the premix chamber, and an oxidant (e.g.,combustion air) channel configured to output the oxidant into the premixchamber. A flame arrestor can be disposed between the premix fuel andoxidant source and the perforated flame holder 102 and be configured toprevent flame flashback into the premix fuel and oxidant source.

The oxidant source 220, whether configured for entrainment in thecombustion volume 204 or for premixing, can include a blower configuredto force the oxidant through the fuel and oxidant source 101.

The support structure 222 can be configured to support the perforatedflame holder 102 from a floor or wall (not shown) of the combustionvolume 204, for example. In another embodiment, the support structure222 supports the perforated flame holder 102 from the fuel and oxidantsource 101. Alternatively, the support structure 222 can suspend theperforated flame holder 102 from an overhead structure (such as a flue,in the case of an up-fired system). The support structure 222 cansupport the perforated flame holder 102 in various orientations anddirections.

The perforated flame holder 102 can include a single perforated flameholder body 208. In another embodiment, the perforated flame holder 102can include a plurality of adjacent perforated flame holder sectionsthat collectively provide a tiled perforated flame holder 102.

The perforated flame holder support structure 222 can be configured tosupport the plurality of perforated flame holder sections. Theperforated flame holder support structure 222 can include a metalsuperalloy, a cementatious, and/or ceramic refractory material. In anembodiment, the plurality of adjacent perforated flame holder sectionscan be joined with a fiber reinforced refractory cement.

The perforated flame holder 102 can have a width dimension W betweenopposite sides of the peripheral surface 216 at least twice a thicknessdimension T between the input face 212 and the output face 214. Inanother embodiment, the perforated flame holder 102 can have a widthdimension W between opposite sides of the peripheral surface 216 atleast three times, at least six times, or at least nine times thethickness dimension T between the input face 212 and the output face 214of the perforated flame holder 102.

In an embodiment, the perforated flame holder 102 can have a widthdimension W less than a width of the combustion volume 204. This canallow the flue gas circulation path 224 from above to below theperforated flame holder 102 to lie between the peripheral surface 216 ofthe perforated flame holder 102 and the combustion volume wall (notshown).

Referring again to both FIGS. 2 and 3, the perforations 210 can be ofvarious shapes. In an embodiment, the perforations 210 can includeelongated squares, each having a transverse dimension D between opposingsides of the squares. In another embodiment, the perforations 210 caninclude elongated hexagons, each having a transverse dimension D betweenopposing sides of the hexagons. In yet another embodiment, theperforations 210 can include hollow cylinders, each having a transversedimension D corresponding to a diameter of the cylinder. In anotherembodiment, the perforations 210 can include truncated cones ortruncated pyramids (e.g., frustums), each having a transverse dimensionD radially symmetric relative to a length axis that extends from theinput face 212 to the output face 214. In some embodiments, theperforations 210 can each have a lateral dimension D equal to or greaterthan a quenching distance of the flame based on standard referenceconditions. Alternatively, the perforations 210 may have lateraldimension D less then than a standard reference quenching distance.

In one range of embodiments, each of the plurality of perforations 210has a lateral dimension D between 0.05 inch and 1.0 inch. Preferably,each of the plurality of perforations 210 has a lateral dimension Dbetween 0.1 inch and 0.5 inch. For example the plurality of perforations210 can each have a lateral dimension D of about 0.2 to 0.4 inch.

The void fraction of a perforated flame holder 102 is defined as thetotal volume of all perforations 210 in a section of the perforatedflame holder 102 divided by a total volume of the perforated flameholder 102 including body 208 and perforations 210. The perforated flameholder 102 should have a void fraction between 0.10 and 0.90. In anembodiment, the perforated flame holder 102 can have a void fractionbetween 0.30 and 0.80. In another embodiment, the perforated flameholder 102 can have a void fraction of about 0.70. Using a void fractionof about 0.70 was found to be especially effective for producing verylow NOx.

The perforated flame holder 102 can be formed from a fiber reinforcedcast refractory material and/or a refractory material such as analuminum silicate material. For example, the perforated flame holder 102can be formed to include mullite or cordierite. Additionally oralternatively, the perforated flame holder body 208 can include a metalsuperalloy such as Inconel or Hastelloy. The perforated flame holderbody 208 can define a honeycomb. Honeycomb is an industrial term of artthat need not strictly refer to a hexagonal cross section and mostusually includes cells of square cross section. Honeycombs of othercross sectional areas are also known.

The inventors have found that the perforated flame holder 102 can beformed from VERSAGRID® ceramic honeycomb, available from AppliedCeramics, Inc. of Doraville, S.C.

The perforations 210 can be parallel to one another and normal to theinput and output faces 212, 214. In another embodiment, the perforations210 can be parallel to one another and formed at an angle relative tothe input and output faces 212, 214. In another embodiment, theperforations 210 can be non-parallel to one another. In anotherembodiment, the perforations 210 can be non-parallel to one another andnon-intersecting. In another embodiment, the perforations 210 can beintersecting. The body 308 can be one piece or can be formed from aplurality of sections.

In another embodiment, which is not necessarily preferred, theperforated flame holder 102 may be formed from reticulated ceramicmaterial. The term “reticulated” refers to a netlike structure.Reticulated ceramic material is often made by dissolving a slurry into asponge of specified porosity, allowing the slurry to harden, and burningaway the sponge and curing the ceramic.

In another embodiment, which is not necessarily preferred, theperforated flame holder 102 may be formed from a ceramic material thathas been punched, bored or cast to create channels.

In another embodiment, the perforated flame holder 102 can include aplurality of tubes or pipes bundled together. The plurality ofperforations 210 can include hollow cylinders and can optionally alsoinclude interstitial spaces between the bundled tubes. In an embodiment,the plurality of tubes can include ceramic tubes. Refractory cement canbe included between the tubes and configured to adhere the tubestogether. In another embodiment, the plurality of tubes can includemetal (e.g., superalloy) tubes. The plurality of tubes can be heldtogether by a metal tension member circumferential to the plurality oftubes and arranged to hold the plurality of tubes together. The metaltension member can include stainless steel, a superalloy metal wire,and/or a superalloy metal band.

The perforated flame holder body 208 can alternatively include stackedperforated sheets of material, each sheet having openings that connectwith openings of subjacent and superjacent sheets. The perforated sheetscan include perforated metal sheets, ceramic sheets and/or expandedsheets. In another embodiment, the perforated flame holder body 208 caninclude discontinuous packing bodies such that the perforations 210 areformed in the interstitial spaces between the discontinuous packingbodies. In one example, the discontinuous packing bodies includestructured packing shapes. In another example, the discontinuous packingbodies include random packing shapes. For example, the discontinuouspacking bodies can include ceramic Raschig ring, ceramic Berl saddles,ceramic Intalox saddles, and/or metal rings or other shapes (e.g. SuperRaschig Rings) that may be held together by a metal cage.

The inventors contemplate various explanations for why burner systemsincluding the perforated flame holder 102 provide such clean combustion.

According to an embodiment, the perforated flame holder 102 may act as aheat source to maintain a combustion reaction even under conditionswhere a combustion reaction would not be stable when supported by aconventional flame holder. This capability can be leveraged to supportcombustion using a leaner fuel-to-oxidant mixture than is typicallyfeasible. Thus, according to an embodiment, at the point where the fuelstream 206 contacts the input face 212 of the perforated flame holder102, an average fuel-to-oxidant ratio of the fuel stream 206 is below a(conventional) lower combustion limit of the fuel component of the fuelstream 206—lower combustion limit defines the lowest concentration offuel at which a fuel and oxidant mixture 206 will burn when exposed to amomentary ignition source under normal atmospheric pressure and anambient temperature of 25° C. (77° F.).

The perforated flame holder 102 and systems including the perforatedflame holder 102 described herein were found to provide substantiallycomplete combustion of CO (single digit ppm down to undetectable,depending on experimental conditions), while supporting low NOx.According to one interpretation, such a performance can be achieved dueto a sufficient mixing used to lower peak flame temperatures (amongother strategies). Flame temperatures tend to peak under slightly richconditions, which can be evident in any diffusion flame that isinsufficiently mixed. By sufficiently mixing, a homogenous and slightlylean mixture can be achieved prior to combustion. This combination canresult in reduced flame temperatures, and thus reduced NOx formation. Inone embodiment, “slightly lean” may refer to 3% O₂, i.e. an equivalenceratio of ˜0.87. Use of even leaner mixtures is possible, but may resultin elevated levels of O₂. Moreover, the inventors believe perforationwalls 308 may act as a heat sink for the combustion fluid. This effectmay alternatively or additionally reduce combustion temperatures andlower NOx.

According to another interpretation, production of NOx can be reduced ifthe combustion reaction 302 occurs over a very short duration of time.Rapid combustion causes the reactants (including oxygen and entrainednitrogen) to be exposed to NOx-formation temperature for a time tooshort for NOx formation kinetics to cause significant production of NOx.The time required for the reactants to pass through the perforated flameholder 102 is very short compared to a conventional flame. The low NOxproduction associated with perforated flame holder combustion may thusbe related to the short duration of time required for the reactants (andentrained nitrogen) to pass through the perforated flame holder 102.

FIG. 4 is a flow chart showing a method 400 for operating a burnersystem including the perforated flame holder shown and described herein.To operate a burner system including a perforated flame holder, theperforated flame holder is first heated to a temperature sufficient tomaintain combustion of the fuel and oxidant mixture.

According to a simplified description, the method 400 begins with step402, wherein the perforated flame holder is preheated to a start-uptemperature, T_(S). After the perforated flame holder is raised to thestart-up temperature, the method proceeds to step 404, wherein the fueland oxidant are provided to the perforated flame holder and combustionis held by the perforated flame holder.

According to a more detailed description, step 402 begins with step 406,wherein start-up energy is provided at the perforated flame holder.

Simultaneously or following providing start-up energy, a decision step408 determines whether the temperature T of the perforated flame holderis at or above the start-up temperature, T_(S). As long as thetemperature of the perforated flame holder is below its start-uptemperature, the method loops between steps 406 and 408 within thepreheat step 402. In step 408, if the temperature T of at least apredetermined portion of the perforated flame holder is greater than orequal to the start-up temperature, the method 400 proceeds to overallstep 404, wherein fuel and oxidant is supplied to and combustion is heldby the perforated flame holder.

Step 404 may be broken down into several discrete steps, at least someof which may occur simultaneously.

Proceeding from step 408, a fuel and oxidant mixture is provided to theperforated flame holder, as shown in step 410. The fuel and oxidant maybe provided by a fuel and oxidant source that includes a separate fuelnozzle and oxidant (e.g., combustion air) source, for example. In thisapproach, the fuel and oxidant are output in one or more directionsselected to cause the fuel and oxidant mixture to be received by theinput face of the perforated flame holder. The fuel may entrain thecombustion air (or alternatively, the combustion air may dilute thefuel) to provide a fuel and oxidant mixture at the input face of theperforated flame holder at a fuel dilution selected for a stablecombustion reaction that can be held within the perforations of theperforated flame holder.

Proceeding to step 412, the combustion reaction is held by theperforated flame holder.

In step 414, heat may be output from the perforated flame holder. Theheat output from the perforated flame holder may be used to power anindustrial process, heat a working fluid, generate electricity, orprovide motive power, for example.

In optional step 416, the presence of combustion may be sensed. Varioussensing approaches have been used and are contemplated by the inventors.Generally, combustion held by the perforated flame holder is very stableand no unusual sensing requirement is placed on the system. Combustionsensing may be performed using an infrared sensor, a video sensor, anultraviolet sensor, a charged species sensor, thermocouple, thermopile,flame rod, and/or other combustion sensing apparatuses. In an additionalor alternative variant of step 416, a pilot flame or other ignitionsource may be provided to cause ignition of the fuel and oxidant mixturein the event combustion is lost at the perforated flame holder.

Proceeding to decision step 418, if combustion is sensed not to bestable, the method 400 may exit to step 424, wherein an error procedureis executed. For example, the error procedure may include turning offfuel flow, re-executing the preheating step 402, outputting an alarmsignal, igniting a stand-by combustion system, or other steps. If, instep 418, combustion in the perforated flame holder is determined to bestable, the method 400 proceeds to decision step 420, wherein it isdetermined if combustion parameters should be changed. If no combustionparameters are to be changed, the method loops (within step 404) back tostep 410, and the combustion process continues. If a change incombustion parameters is indicated, the method 400 proceeds to step 422,wherein the combustion parameter change is executed. After changing thecombustion parameter(s), the method loops (within step 404) back to step410, and combustion continues.

Combustion parameters may be scheduled to be changed, for example, if achange in heat demand is encountered. For example, if less heat isrequired (e.g., due to decreased electricity demand, decreased motivepower requirement, or lower industrial process throughput), the fuel andoxidant flow rate may be decreased in step 422. Conversely, if heatdemand is increased, then fuel and oxidant flow may be increased.Additionally or alternatively, if the combustion system is in a start-upmode, then fuel and oxidant flow may be gradually increased to theperforated flame holder over one or more iterations of the loop withinstep 404.

Referring again to FIG. 2, the burner system 200 includes a heater 228operatively coupled to the perforated flame holder 102. As described inconjunction with FIGS. 3 and 4, the perforated flame holder 102 operatesby outputting heat to the incoming fuel and oxidant mixture 206. Aftercombustion is established, this heat is provided by the combustionreaction 302; but before combustion is established, the heat is providedby the heater 228.

Various heating apparatuses have been used and are contemplated by theinventors. In some embodiments, the heater 228 can include a flameholder configured to support a flame disposed to heat the perforatedflame holder 102. The fuel and oxidant source 101 can include a fuelnozzle 218 configured to emit a fuel stream 206 and an oxidant source220 configured to output oxidant (e.g., combustion air) adjacent to thefuel stream 206. The fuel nozzle 218 and oxidant source 220 can beconfigured to output the fuel stream 206 to be progressively diluted bythe oxidant (e.g., combustion air). The perforated flame holder 102 canbe disposed to receive a diluted fuel and oxidant mixture 206 thatsupports a combustion reaction 302 that is stabilized by the perforatedflame holder 102 when the perforated flame holder 102 is at an operatingtemperature. A start-up flame holder, in contrast, can be configured tosupport a start-up flame at a location corresponding to a relativelyunmixed fuel and oxidant mixture that is stable without stabilizationprovided by the heated perforated flame holder 102.

The burner system 200 can further include a controller 103 operativelycoupled to the heater 228 and to a data interface 232. For example, thecontroller 103 can be configured to control a start-up flame holderactuator configured to cause the start-up flame holder to hold thestart-up flame when the perforated flame holder 102 needs to bepre-heated and to not hold the start-up flame when the perforated flameholder 102 is at an operating temperature (e.g., when T≥T_(S)).

Various approaches for actuating a start-up flame are contemplated. Inone embodiment, the start-up flame holder includes amechanically-actuated bluff body configured to be actuated to interceptthe fuel and oxidant mixture 206 to cause heat-recycling and/orstabilizing vortices and thereby hold a start-up flame; or to beactuated to not intercept the fuel and oxidant mixture 206 to cause thefuel and oxidant mixture 206 to proceed to the perforated flame holder102. In another embodiment, a fuel control valve, blower, and/or dampermay be used to select a fuel and oxidant mixture flow rate that issufficiently low for a start-up flame to be jet-stabilized; and uponreaching a perforated flame holder 102 operating temperature, the flowrate may be increased to “blow out” the start-up flame. In anotherembodiment, the heater 228 may include an electrical power supplyoperatively coupled to the controller 103 and configured to apply anelectrical charge or voltage to the fuel and oxidant mixture 206. Anelectrically conductive start-up flame holder may be selectively coupledto a voltage ground or other voltage selected to attract the electricalcharge in the fuel and oxidant mixture 206. The attraction of theelectrical charge was found by the inventors to cause a start-up flameto be held by the electrically conductive start-up flame holder.

In another embodiment, the heater 228 may include an electricalresistance heater configured to output heat to the perforated flameholder 102 and/or to the fuel and oxidant mixture 206. The electricalresistance heater can be configured to heat up the perforated flameholder 102 to an operating temperature. The heater 228 can furtherinclude a power supply and a switch operable, under control of thecontroller 103, to selectively couple the power supply to the electricalresistance heater.

An electrical resistance heater 228 can be formed in various ways. Forexample, the electrical resistance heater 228 can be formed fromKANTHAL® wire (available from Sandvik Materials Technology division ofSandvik AB of Hallstahammar, Sweden) threaded through at least a portionof the perforations 210 defined by the perforated flame holder body 208.Alternatively, the heater 228 can include an inductive heater, ahigh-energy beam heater (e.g. microwave or laser), a frictional heater,electro-resistive ceramic coatings, or other types of heatingtechnologies.

Other forms of start-up apparatuses are contemplated. For example, theheater 228 can include an electrical discharge igniter or hot surfaceigniter configured to output a pulsed ignition to the oxidant and fuel.Additionally or alternatively, a start-up apparatus can include a pilotflame apparatus disposed to ignite the fuel and oxidant mixture 206 thatwould otherwise enter the perforated flame holder 102. The electricaldischarge igniter, hot surface igniter, and/or pilot flame apparatus canbe operatively coupled to the controller 103, which can cause theelectrical discharge igniter or pilot flame apparatus to maintaincombustion of the fuel and oxidant mixture 206 in or upstream from theperforated flame holder 102 before the perforated flame holder 102 isheated sufficiently to maintain combustion.

The burner system 200 can further include a sensor 234 operativelycoupled to the control circuit 103. The sensor 234 can include a heatsensor configured to detect infrared radiation or a temperature of theperforated flame holder 102. The control circuit 103 can be configuredto control the heating apparatus 228 responsive to input from the sensor234. Optionally, a fuel control valve 236 can be operatively coupled tothe controller 103 and configured to control a flow of fuel to the fueland oxidant source 101. Additionally or alternatively, an oxidant bloweror damper 238 can be operatively coupled to the controller 103 andconfigured to control flow of the oxidant (or combustion air). Thesensor 234 can further include a combustion sensor operatively coupledto the control circuit 103, the combustion sensor being configured todetect a temperature, video image, and/or spectral characteristic of acombustion reaction 302 held by the perforated flame holder 102. Thefuel control valve 236 can be configured to control a flow of fuel froma fuel source to the fuel and oxidant source 202. The controller 103 canbe configured to control the fuel control valve 236 responsive to inputfrom the combustion sensor 234. The controller 103 can be configured tocontrol the fuel control valve 236 and/or oxidant blower or damper tocontrol a preheat flame type of heater 228 to heat the perforated flameholder 102 to an operating temperature. The controller 103 can similarlycontrol the fuel control valve 236 and/or the oxidant blower or damperto change the fuel and oxidant mixture 206 flow responsive to a heatdemand change received as data via the data interface 232.

FIG. 5A is a diagram of a combustion system 500, according to anembodiment. The combustion system 500 includes a fuel and oxidant source101, a perforated flame holder 102, a control circuit 103, an imagecapture device 105, and a memory 107.

According to an embodiment, the fuel and oxidant source 101 includes,for example, a fuel nozzle configured to output fuel and oxidant ontothe perforated flame holder 102. The perforated flame holder 102sustains a combustion reaction of the fuel and oxidant primarily withinthe perforated flame holder 102. The control circuit 103 is configuredto cause the image capture device 105 to capture one or more images ofthe combustion reaction. In one embodiment, the control circuit isfurther configured to analyze the one or more images and to adjust thecharacteristics of the combustion reaction based on the analysis of theone or more images.

In FIG. 5B the fuel and oxidant source 101 is outputting fuel andoxidant 504 onto the perforated flame holder 102, according to anembodiment. The perforated flame holder 102 holds a combustion reaction502 of the fuel and oxidant 504. The image capture device 105 capturesan image of the combustion reaction 502 in the position shown in FIG.5B. In FIG. 5B the combustion reaction 502 is mostly confined within theperforations of the perforated flame holder 102. However, a portion ofthe combustion reaction 502 is below the perforated flame holder 102 anda portion of the combustion reaction 502 is above the perforated flameholder 102. The image capture device 105 outputs the captured image ofthe combustion reaction 502 to the control circuit 103. The controlcircuit 103 stores the captured image in the memory 107.

In FIG. 5C the fuel and oxidant source 101 is outputting fuel andoxidant 504 onto the perforated flame holder 102. The perforated flameholder 102 holds a combustion reaction 502 of the fuel and oxidant 504.The image capture device 105 captures an image of the combustionreaction 502 in the position shown in FIG. 5C. In FIG. 5C the combustionreaction 502 is mostly confined within the perforations of theperforated flame holder 102. A smaller portion of the combustionreaction 502 is below the perforated flame holder 102 than in FIG. 5B.The image capture device 105 outputs the captured image of thecombustion reaction 502 to the control circuit 103. The control circuit103 stores the captured image in the memory 107.

In FIG. 5D the fuel and oxidant source 101 is outputting fuel andoxidant 504 onto the perforated flame holder 102, according to anembodiment. The perforated flame holder 102 holds a combustion reaction502 of the fuel and oxidant 504. The image capture device 105 capturesan image of the combustion reaction 502 in the position shown in FIG.5D. In FIG. 5D the combustion reaction 502 is mostly confined within theperforations of the perforated flame holder 102. A larger portion of thecombustion reaction 502 is below the perforated flame holder 102 than inFIG. 5B, 5C. The image capture device 105 outputs the captured image ofthe combustion reaction 502 to the control circuit 103. The controlcircuit 103 stores the captured image in the memory 107.

FIG. 5E is an averaged image 506 of the combustion reaction 502 producedfrom the combustion reaction 102 images of FIGS. 5B-5D, according to oneembodiment. The control circuit 103 receives the images of thecombustion reaction 502 corresponding to FIGS. 5B-5D from the imagecapture device 105. The control circuit 103 produces from the images ofthe combustion reaction 502 the averaged image 506 of the combustionreaction 502 shown in dashed lines in FIG. 5E. The averaged image 506 ofthe combustion reaction 502 shows the average position of the combustionreaction 502 from the images captured by the camera 105.

While the averaged image 506 has been described as being produced fromthree images of the combustion reaction 502, in practice the averagedimage 506 can be produced from dozens or hundreds of images of thecombustion reaction 502.

After the averaged image 506 has been produced, the control circuit 103compares the averaged image 506 to one or more reference images storedin the memory 107. The reference images can correspond to particulartarget combustion reaction 502 profiles that can be selected for thecombustion reaction 502.

While FIGS. 5A-5E have disclosed an embodiment in which the imagecapture device 105 captures a visible spectrum image that indicates theposition of the combustion reaction 502 with respect to the perforatedflame holder 102, the image capture device 105 can capture other typesof images to provide indications of other characteristics of thecombustion reaction 502. For example, the image capture device 105 cancapture an image that indicates heat or temperature distributions of thecombustion reaction, the perforated flame holder 102, and the fuel andoxidant 504. If the captured image indicates that the fuel and oxidantbelow the perforated flame holder 102 are very hot, this can indicatethat the fuel and oxidant will soon combust below the perforated flameholder 102 rather than within the perforated flame holder 102. In thiscase, the control circuit 103, or a technician, can cause the fuel andoxidant source 101 to alter the output of fuel and oxidant 504 in such away to reduce the heat of the fuel and oxidant below the perforatedflame holder 102. Alternatively, the captured image can indicate thatthe perforated flame holder 102 is not evenly heated i.e. that thecombustion reaction 502 now be taking place within some portions of theperforated flame holder 102. This can indicate that the fuel and oxidantare not being evenly distributed into the perforated flame holder 102.In response, the control circuit 103, or a technician, can adjust theoutput of fuel and oxidant from the fuel and oxidant source 101.Alternatively, the captured image can indicate that the combustionreaction is very blue near the top of the perforated flame holder 102.This can be an indication that a significant portion of the combustionreaction 504 is occurring above the perforated flame holder 102 in theform of blue flame, or that the perforated flame holder 102 is too hot.Accordingly, the control circuit 103 or technician can adjust the outputof fuel and oxidant 504 from the fuel and oxidant source 101 to adjustthe combustion reaction 502. In one embodiment, the control circuit 103can adjust the combustion reaction 502 by reducing the heat load, forexample by reducing water flow to steam tubes. In one embodiment thefuel and oxidant source 101 can include one or more fuel nozzles eachhaving one or more orifices. The control circuit 103 can reduce fuelvelocity by switching to larger orifice nozzles or by outputting thesame amount of fuel through more nozzles. In one embodiment the controlcircuit can change the fuel mix to a higher speed fuel, for example byadding hydrogen.

According to an embodiment, the one or more images can indicate that thecombustion reaction 502 is closer than desired to the fuel and oxidantsource 101. In some cases that can be tolerable. In other cases thecontrol circuit 103 will adjust the output of the fuel and oxidant 504to cause the combustion reaction 502 to retract from the fuel andoxidant source 101, for example by increasing fuel velocity or byswitching to a fuel mixture having a lower flame speed. Alternatively,the fuel control circuit 103 can shut off the output of the fuel fromthe fuel and oxidant source 101 to stop the combustion reactionentirely.

FIG. 6A is a diagram of a combustion system 600, according to anembodiment. The combustion system 600 includes a fuel and oxidant source101, a perforated flame holder 102, a control circuit 103, anelectrocapacitive tomography device 605, and a memory 107.

According to an embodiment, the fuel and oxidant source 101 includes,for example, a fuel nozzle configured to output fuel and oxidant ontothe perforated flame holder 102. The perforated flame holder 102sustains a combustion reaction of the fuel and oxidant primarily withinthe perforated flame holder 102.

According to an embodiment, the electrocapacitive tomography device 605is an image capture device that includes a plurality of electrodes 620positioned at selected locations adjacent to the perforated flame holder102. The electrocapacitive tomography device 605 is configured to makeimages of the perforated flame holder 102 based on the capacitancebetween the electrodes 620. The images represent slices of theperforated flame holder 102 based on the capacitances between theelectrodes 620. The capacitance between pairs of electrodes 620 depends,in part, on the dielectric constant of the material(s) between the pairsof electrodes 620. In particular, the dielectric constant within theperforations of the perforated flame holder 102 can change based on thecharacteristics of the combustion reaction within the perforations.Therefore, the images produced by the electrical tomography device 605can give an indication of a temperature within the perforations or aconcentration or flow of fuel, oxidant, and flue gasses at variouslocations in the perforated flame holder 102 based on the dielectricconstant at the various locations of the perforated flame holder 102.

The control circuit 103 can analyze the images and adjust the combustionreaction based on the images.

According to an embodiment, the control circuit 103 is configured tocause the electrocapacitive tomography device 605 to capture one or moreimages of the combustion reaction. In one embodiment, the controlcircuit 103 is further configured to analyze the one or more images andto adjust the characteristics of the combustion reaction based on theanalysis of the one or more images.

FIG. 6B is a top view of the perforated flame holder 102 and theelectrocapacitive tomography device 605, according to an embodiment. Theelectrocapacitive tomography device 605 includes multiple pairs ofelectrodes 620 positioned laterally around the perforated flame holder102. Each pair of electrodes 620 includes two electrodes 620 directlyfacing each other, with the perforated flame holder 102 positionedbetween the pair of electrodes. The control circuit 103 controls eachpair of electrodes 620 to make a plurality of images of the perforatedflame holder 102, according to an embodiment.

In one embodiment, the electrodes 620 a and 620 a are a pair, theelectrodes 620 b are a pair, the electrodes 620 c are a pair, theelectrodes 620 d are a pair, the electrodes 620 e are a pair, and theelectrodes 620 f are a pair. The electrocapacitive tomography device 605can generate the electrocapacitive tomography images based on acapacitance between the pairs of electrodes.

In one embodiment, the plurality of electrodes 620 includes one or morefirst pairs of electrodes facing each other in a first orientationsubstantially perpendicular to a primary direction of a flow of the fueland oxidant toward the perforated flame holder. In one example, thefirst pairs of electrodes can include the pair of electrodes 620 a andthe pair of electrodes 620 b. The first pairs of electrodes sense thecapacitance of the perforated flame holder along an X directionsubstantially perpendicular to a primary direction of flow of the fueland oxidant toward the perforated flame holder. The primary direction offlow of the fuel and oxidant toward the perforated flame holder 102 cancorrespond to a Z direction.

In one embodiment, the plurality of electrodes 620 includes one or moresecond pairs of electrodes facing each other in a second orientationsubstantially perpendicular to the first orientation and a primarydirection of a flow of the fuel and oxidant toward the perforated flameholder. In one example, the second pairs of electrodes can include thepair of electrodes 620 c and the pair of electrodes 620 d. The secondpairs of electrodes sense the capacitance of the perforated flame holder102 along a Y direction substantially perpendicular to the primarydirection of flow of the fuel and oxidant and substantiallyperpendicular to orientation of the pairs of electrodes 620 a and 620 b.

In one embodiment, the plurality of electrodes can include pairs ofelectrodes oriented transverse to both the first pairs of electrodes andthe second pairs of electrodes. The transverse pairs of electrodes caninclude the pair of electrodes 620 e and the pair of electrodes 620 f.

FIG. 7A is a diagram of a combustion system 700, according to anembodiment. The combustion system 700 includes a fuel and oxidant source101, a perforated flame holder 102, a control circuit 103, amagnetic-inductive tomography device 705, and a memory 107.

According to an embodiment, the fuel and oxidant source 101 includes,for example, a fuel nozzle configured to output fuel and oxidant ontothe perforated flame holder 102. The perforated flame holder 102sustains a combustion reaction of the fuel and oxidant primarily withinthe perforated flame holder 102.

According to an embodiment, the electromagnetic induction tomographydevice 705 is an image capture device that includes a plurality ofinductor coils 720 positioned at selected locations adjacent to theperforated flame holder 102. The electromagnetic induction tomographydevice 705 is configured to make images of the perforated flame holder102 based on induction characteristics between pairs of inductor coils720. In particular, each pair of inductor coils 720 includes anexcitation coil and the sensing coil. The excitation coil is excited togenerate a magnetic field. The magnetic field induces eddy currentswithin the perforations of the perforated flame holder 102 or within thebody of the perforated flame holder 102. The sensing coil detects theeddy currents by sensing magnetic fields generated by the eddy currents.The eddy currents are dependent, in part, on the conductivity,permittivity, and permeability of the material(s) between the pairs ofinductor coils 720. The conductivity, permittivity, and permeability ofthe material(s) within the perforations of the perforated flame holder102 can change based on the characteristics of the combustion reactionwithin the perforations. Therefore, the images produced by theelectromagnetic induction tomography device 705 can give an indicationof a temperature within the perforations or a concentration or flow offuel, oxidant, and flue gasses at various locations in the perforatedflame holder 102 based on the dielectric constant at the variouslocations of the perforated flame holder 102. The control circuit 103can analyze the images and adjust the combustion reaction based on theimages.

According to an embodiment, the control circuit 103 is configured tocause the electromagnetic induction tomography device 705 to capture oneor more images of the combustion reaction. In one embodiment, thecontrol circuit 103 is further configured to analyze the one or moreimages and to adjust the characteristics of the combustion reactionbased on the analysis of the one or more images.

While FIG. 7A shows only a single wire connected between each inductorcoil 720 and the control circuit 103, in practice two wires may becoupled between each inductor coil and the control circuit 103. This isbecause each could may include two terminals.

FIG. 7B is a top view of the perforated flame holder 102 and theelectromagnetic induction tomography device 705, according to anembodiment. The electromagnetic induction tomography device 705 includesmultiple pairs of inductor coils 720 positioned laterally around theperforated flame holder 102. Each pair of inductor coils 720 includestwo inductor coils 720 directly facing each other. In each pair ofinductor coils 720, one inductor coil 720 acts as an excitation coil andthe other inductor coil 720 acts as a sensing coil. The control circuit103 controls each pair of inductor coils 720 to make a plurality ofimages of the perforated flame holder 102, according to an embodiment.

FIG. 7C is a side view of an inductor coil 720 of the electromagneticinduction tomography device 705, according to an embodiment. Theinductor coils 720 include a conductive wire or other conductivematerial with several windings and two terminals. Each terminal isconnected to the control circuit 103.

FIG. 8A is a side sectional view of a portion of a perforated flameholder 102 and an electroresistive tomography device 805, according toan embodiment.

According to an embodiment, the electroresistive tomography device 805is an image capture device that can include a plurality of electrodes820 positioned within the perforations of the perforated flame holder102. A pair of electrodes 820 is positioned within each perforation 210of the perforated flame holder 102. Each electrode 820 may be coupled toa conductive wire 822. The electroresistive tomography device 805 isconfigured to make images of the perforated flame holder 102 based onthe resistance between pairs of electrodes 820. The control circuit 103applies a voltage between each pair of electrodes 820. Theelectroresistive image capture device 805 makes a plurality of imagesbased on the resistances of the materials within the perforations 210.The resistance of the materials within the perforations 210 can changebased on the characteristics of the combustion reaction within theperforations 210. Therefore, the images produced by the electroresistivetomography device 805 can give an indication of a temperature within theperforations 210 or a concentration or flow of fuel, oxidant, and fluegasses at various locations in the perforated flame holder 102 based onthe resistance at the various locations of the perforated flame holder102. The control circuit 103 can analyze the images and adjust thecombustion reaction based on the images.

According to an embodiment, the control circuit 103 is configured tocause the electroresistive tomography device 805 to capture one or moreimages of the combustion reaction. In one embodiment, the controlcircuit 103 is further configured to analyze the one or more images andto adjust the characteristics of the combustion reaction based on theanalysis of the one or more images.

FIG. 8B is a perspective view of a portion of a perforated flame holder102 including an electro resistive tomography device 805, according toan embodiment. A plurality of electrodes 820 are positioned within theperforations 210 of the perforated flame holder 102 and coupled toconductive wires 822 that extend along the top surface of the perforatedflame holder 102. The electrodes 820 are each coupled to a wire 822. Forsimplicity, FIG. 8B depicts multiple electrodes 820 coupled to a singlewire 822, in practice each electrode 820 may be coupled to a differentwire 822 that extends along the top surface of the perforated flameholder 102, so that the resistance in each perforation 210 may bemeasured individually. The wires 822 can be coupled to the controlcircuit 103. The control circuit 103 can apply a voltage between eachpair of electrodes 820 in order to determine the resistance of eachperforation 210, generating an image of the perforated flame holder 102based on the resistances.

FIG. 9 is a diagram of a combustion system 500, according to anembodiment. The combustion system 500 includes a fuel and oxidant source101, a perforated flame holder 102, a control circuit 103, an imagecapture device 105, and a memory 107. The combustion system 500 furtherincludes a hydrogen source 922 coupled to the fuel and oxidant source101 by a valve 924. The control circuit 103 can control the operation ofthe valve 924 to allow more or less hydrogen to be output from the fueland oxidant source 101.

According to an embodiment, the fuel and oxidant source 101 includes,for example, a fuel nozzle configured to output fuel and oxidant ontothe perforated flame holder 102. The perforated flame holder 102sustains a combustion reaction of the fuel and oxidant primarily withinthe perforated flame holder 102. The control circuit 103 is configuredto cause the image capture device 105 to capture one or more images ofthe combustion reaction. In one embodiment, the control circuit 103 isfurther configured to analyze the one or more images and to adjust thecharacteristics of the combustion reaction based on the analysis of theone or more images.

According to an embodiment, the control circuit 103 adjusts thecharacteristics of the combustion reaction by adjusting the valve 924 toprovide more or less hydrogen to the fuel and oxidant source 101. In oneexample, when the perforated flame holder 102 appears darker based onthe image or images, the control circuit 103 can actuate the valve 924to add hydrogen to the fuel in order to pull the combustion reactionback down within the perforated flame holder 102. Additionally oralternatively, when the perforated flame holder 102 appears dark, thecontrol circuit 103 can activate a valve 924 to switch to a largercumulative fuel nozzle orifice cross-sectional area in order to reducefuel velocity. This also will help pull the combustion reaction downinto the perforated flame holder 102. Alternatively, the control circuit103 can output a signal or message that indicates to a technician tomanually operate the valve 924 to adjust the amount of hydrogen suppliedto the fuel and oxidant source 101 or to manually operate a valve orother mechanisms to increase or decrease the cumulative fuel nozzleorifice cross-sectional area.

While the fuel and oxidant source 101 and the hydrogen source 922 aredepicted as being separate in FIG. 9, in practice the hydrogen source922 and the valve 924 can be a part of the fuel and oxidant source 101.

FIG. 10 is a graph illustrating the relative intensity I of light outputfrom the perforated flame holder 102 and/or the combustion reaction as afunction of the frequency f of light. Two curves are shown in FIG. 10for two different temperatures of perforated flame holder 102. At afirst lower temperature T1, the peak intensity occurs at a frequency f1.At a second higher temperature T2, the peak intensity occurs at afrequency f2. Thus, as the temperature increases, the peak intensityoccurs at a high frequency of light (more blue). The control circuit 103can determine what is the temperature of the perforated flame holder 102based on the distribution of various frequencies of emitted light ascaptured in the images. The control circuit 103 can then adjust theparameters of the combustion reaction accordingly. While FIG. 10 isdescribed in relation to frequencies of emitted light, more commonly thewavelength A of light may be measured/analyzed. The wavelength λ andfrequency f of light are related to each other, and to the speed oflight c, by the equation:

λ=c/f.

FIG. 11 is a flow diagram of a process 1100 for operating a combustionsystem, according to an embodiment. At 1102, the fuel and oxidant sourceoutputs fuel and oxidant onto a perforated flame holder. At 1104 theperforated flame holder supports a combustion reaction of the fuel andoxidant within the perforations of the perforated flame holder. At 1106,the image capture device captures one or more images of the combustionreaction. At 1108 the combustion reaction is adjusted based on the oneor more images. The combustion reaction can be adjusted by a controlcircuit or by a technician. The combustion reaction can be adjusted, forexample, by adjusting the output of fuel and oxidant onto the perforatedflame holder. This can be done automatically by the control circuit, ormanually by a technician, according to an embodiment.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments are contemplated. The various aspects andembodiments disclosed herein are for purposes of illustration and arenot intended to be limiting, with the true scope and spirit beingindicated by the following claims.

What is claimed is:
 1. A system, comprising: a fuel and oxidant sourceconfigured to output fuel and oxidant; a perforated flame holderdisposed to receive the fuel and oxidant and configured to sustain acombustion reaction of the fuel and oxidant primarily within theperforated flame holder; an electrocapacitive tomography deviceconfigured to capture a plurality of electrocapacitive tomography imagesof the combustion reaction; and a control circuit configured to producefrom the plurality of electrocapacitive tomography images an averagedimage of the combustion reaction.
 2. The system of claim 1, wherein theelectrocapacitive tomography device includes a plurality of electrodespositioned laterally around the perforated flame holder.
 3. The systemof claim 2, wherein the plurality of electrodes include one or morepairs of electrodes separated from each other by the perforated flameholder.
 4. The system of claim 3, wherein the electrocapacitivetomography device generates the electrocapacitive tomography imagesbased on a capacitance between the one or more pairs of electrodes. 5.The system of claim 2, wherein the plurality of electrodes includes oneor more first pairs of electrodes separated from each other by theperforated flame holder and facing each other in a first orientationsubstantially perpendicular to a primary direction of a flow of the fueland oxidant toward the perforated flame holder.
 6. The system of claim5, wherein the plurality of electrodes includes one or more second pairsof electrodes separated from each other by the perforated flame holderand facing each other in a second orientation substantiallyperpendicular to both the first orientation and the primary direction ofthe flow of the fuel and oxidant.
 7. A combustion system, comprising: afuel and oxidant source configured to output fuel and oxidant; aperforated flame holder including: an input face positioned proximal tothe fuel and oxidant source and configured to receive the fuel andoxidant; an output face positioned distal to the fuel and oxidantsource; and a plurality of perforations extending between the input faceand the output face and configured to support a majority of thecombustion reaction within the perforations; and an image capture devicepositioned to capture an image of the combustion reaction.
 8. Thecombustion system of claim 7, wherein the image indicates a heatdistribution of the combustion reaction.
 9. The combustion system ofclaim 8, wherein the image indicates a heat distribution of theperforated flame holder.
 10. The combustion system of claim 7,comprising a control circuit communicatively coupled to the imagecapture device and the fuel and oxidant source.
 11. The combustionsystem of claim 10, wherein the control circuit is configured to receivethe image from the image capture device.
 12. The combustion system ofclaim 11, wherein the control circuit is configured to adjust thecombustion reaction based on the image.
 13. The combustion system ofclaim 12, wherein the control circuit is configured to adjust thecombustion reaction by adjusting an output of the fuel and oxidant fromthe fuel and oxidant source.
 14. The combustion reaction of claim 13,wherein the image indicates that a significant portion of the combustionreaction is blue flame occurring above the perforated flame holder andthe control circuit is configured to adjust the combustion reaction toreduce an amount of blue flame occurring above the perforated flameholder.
 15. The combustion system of claim 13, wherein the fuel andoxidant source includes a fuel nozzle.
 16. The combustion system ofclaim 15, wherein the fuel and oxidant source includes multiple fuelnozzles.
 17. The combustion system of claim 16, wherein adjusting theoutput of the fuel and oxidant includes adjusting a number of fuelnozzles from which the fuel is output.
 18. The combustion system ofclaim 17, wherein the adjusting the output of fuel and oxidant includesoutputting fuel from one or more fuel nozzles that were not active priorto analyzing the image.
 19. The combustion system of claim 13, furthercomprising: a hydrogen source; and a valve coupling the hydrogen sourceto the fuel and oxidant source.
 20. The combustion system of claim 19,wherein the control circuit is configured to operate the valve toincrease an amount of hydrogen output by the fuel and oxidant sourcebased on a darkness of the image.
 21. The combustion system of claim 20,wherein the control circuit is configured to operate the valve toincrease the amount of hydrogen output by the fuel and oxidant sourcewhen the image indicates that the combustion reaction is above theperforated flame holder.
 22. The combustion system of claim 19, whereinthe control circuit is configured to output a signal that indicates thata technician should operate the valve to adjust an amount of hydrogenoutput by the fuel and oxidant source based on the image.
 23. Thecombustion system of claim 10, wherein the image capture device includesan electrocapacitive tomography device.
 24. The combustion system ofclaim 23, wherein the electrocapacitive tomography device includes aplurality of electrodes positioned laterally around the perforated flameholder.
 25. The combustion system of claim 10, wherein the image capturedevice includes an electromagnetic induction tomography device.
 26. Thecombustion system of claim 25, wherein the electromagnetic inductiontomography device includes a plurality of inductor coils positionedlaterally around the perforated flame holder.
 27. The combustion systemof claim 10, wherein the image capture device includes anelectroresistive tomography device.
 28. The combustion system of claim27, wherein the electroresistive tomography device includes a pluralityof electrodes positioned within the perforations of the perforated flameholder.
 29. A method, comprising: outputting fuel and oxidant from afuel and oxidant source onto a perforated flame holder; supporting acombustion reaction of the fuel and oxidant primarily within theperforated flame holder; capturing an image of the combustion reactionwith an image capture device; and adjusting the combustion reactionbased on the image.
 30. The method of claim 29, comprising: passing theimage to a control circuit; and adjusting the combustion reaction byaltering, with the control circuit, the output of fuel and oxidant fromthe fuel and oxidant source.
 31. The method of claim 30, comprisinganalyzing, with the control circuit, the image.
 32. The method of claim31, comprising adjusting the combustion reaction based on the analysisof the image.
 33. The method of claim 32, wherein analyzing the imageincludes analyzing multiple images.
 34. The method of claim 32, whereinanalyzing the image includes analyzing an averaged image produced frommultiple images of the combustion reaction.
 35. The method of claim 29,wherein adjusting the combustion reaction includes stopping the outputof fuel from the fuel and oxidant source.
 36. The method of claim 29,wherein the image capture device is an electrocapacitive tomographyimage capture device including a plurality of electrodes positionedadjacent to the perforated flame holder.
 37. The method of claim 36,wherein capturing an image includes capturing a plurality ofelectrocapacitive tomography images of the perforated flame holder.